Sangoma SBC 2.3.23-119-GA Unauthenticated User Creation

`## Introduction  
  
### Description  
  
A remotely exploitable vulnerability exists in the 2.3.23-119-GA version of Sangoma SBC that would allow an unauthenticated user to create a privileged user on the system using the web application login interface.  
  
### Vulnerability Type  
  
- Argument Injection or Modification (https://cwe.mitre.org/data/definitions/88.html)  
  
## Product Overview  
  
A Sangoma SBC protects both your data and voice network and is designed to handle every aspect of phone calls that travel over the internet (or voice-over-ip phone calls).  
  
## Background  
  
The Sangoma SBC web application heavily relies on the python script `/usr/local/sng/bin/sng-user-mgmt` for various user operations including authenticating the user that is supplied on the login screen of the web application.  
  
When a username and password is provided to the application, it is processed by `/var/webconfig/gui/Webconfig.inc.php` which uses the `Execute` function from `/var/webconfig/api/ShellExec.class.php` to pass the credentials to `/usr/local/sng/bin/sng-user-mgmt` as arguments. The `Execute` function applies the `escapeshellcmd` function to convert any shell characters as literals, however there is no verification that the variables passed do not contain strings that can be interpreted as additional arguments to `/usr/local/sng/bin/sng-user-mgmt`.  
  
For example, when a username `root` and password `secure` is passed to the application, the final command that is created by `Execute` to be run is `/usr/local/sng/bin/sng-user-mgmt --action=login --user=ha --encrypted-password=ENCPASS(secure)`  
  
By inspecting the code and help menu of `/usr/local/sng/bin/sng-user-mgmt`, we see that the `action` parameter supports other modes which includes `add` that creates a user. The `-o` option can be used to make the user have sudo privileges when `--action=add` is used.  
  
Passing additional arguments through the username field results in a new privileged user being created on the system.  
  
## Proof of Concept Exploit  
  
1. Pass a username with the value `john --action=add -p StrongPass1 -o`  
2. The password field can be set to anything as this will be ignored  
3. Click login  
4. A local user with sudo privileges called `john` with password `StrongPass1` will be created  
5. An attacker can SSH into the machine with these credentials or login via the web console  
  
## Versions Tested  
  
- 2.3.23-119-GA  
  
## Vendor Response  
  
This issue has been responsibly disclosed to the vendor for which a patch has been released in version 2.3.24  
  
https://wiki.sangoma.com/display/SBC/SBC+Downloads  
  
## Credits  
  
Appsecco Security Team  
http://www.appsecco.com  
  
## Timeline  
  
18th May 2019: Discovered and reported to vendor  
21st May 2019: Vendor confirmation  
23rd July 2019: Fixed version (2.3.24) released  
  
## Reference  
  
- [https://www.sangoma.com/products/sbc/](https://www.sangoma.com/products/sbc/)  
  
  
Riyaz Walikar  
  
+91 9886042242  
  
<http://www.appsecco.com/>www.appsecco.com<http://www.appsecco.com/>  
  
Appsecco is a registered trademark of Appsecco Ltd. Appsecco Limited: Registration Number: 9500721. Registered office: Kemp House, 152 to 160 City Road, London EC1V 2NX, United Kingdom. This email message is intended for the named recipient only. It may be privileged and/or confidential. If you are not the named recipient of this email please notify us immediately and do not copy it or use it for any purpose, nor disclose its contents to any other person.  
  
  
  
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